1. Field of the Invention
This invention relates in general to the field of array microscopy and, in particular, to the use of variable-focus liquid lenses for providing programmable optics to correct aberrations, ensure uniform performance of the array, and focus dynamically during the scan of uneven surfaces.
2. Description of the Prior Art
Array microscopes image a sample surface by scanning linearly over the sample. The microscopes of the array acquire intensity data corresponding to adjacent strips of the sample surface, thereby providing a complete image of the sample with a single scan. Each microscope consists of a fixed combination of optical elements with the same design characteristics. Accordingly, each microscope exhibits the same optical performance, subject to tolerances and imperfections of manufacture, aberrations, and other variables. Therefore, such an array of passive imaging elements suffers from the limitation that its finite area is greater than the local variation of topography on the sample being scanned. For example, tissue mounted on a glass slide may exhibit topography changes that occur over a distance shorter than the width of the array. In that case, some of the imaging elements may be unable to focus on the tissue despite available degrees of freedom of the scanning mechanism, such as pitch, roll and vertical translation. A typical array microscope is described in U.S. Ser. No. 10/637,486.
It would be very desirable to provide independent focusing and/or corrective functionality to each microscope of the array. Such functionality may be provided with the use of a liquid-lens component in each microscope of the array. Current approaches for implementing variable liquid lenses are based on the use of three different electrowetting topologies, as illustrated in FIG. 1. The first approach, FIG. 1(a), was developed by Joseph Fourier University (see U.S. Pat. No. 6,369,954) and consists of a tubular structure C defining a lens cell connecting two annular, parallel, electrode plates, 2 and 4, positioned between two, polar and non-polar, immiscible liquids, l1 and l2, with different refractive indices. A lens meniscus M is formed in the structure C at the interface between the two liquids. The second approach, illustrated in two alternative embodiments in FIG. 1(b) and described in Olympus' U.S. Pat. No. 6,934,090, uses a tubular structure C connecting two axially stacked electrode cylinders, 6 and 8 (or 8′), placed about the two liquids l1, and l2. Yet a third configuration, described in Philips' U.S. Pat. No. 7,126,903, uses a combination of the two approaches with the tubular structure C connecting a cylinder 8 aligned axially with an annular plate 2, as shown in FIG. 1(c). This configuration has been implemented in a variable-focus camera/phone device described by B. Hendriks et al, in an article entitled “Through a Lens Sharply,” IEEE Spectrum, December 2004, pages 32-36. This article also proposes the segmentation of the top electrode in order to tilt the meniscus and thus enabling imaging in directions at an angle with the lens axis.
The present invention builds upon this prior art with a novel approach that affords a greater degree of flexibility than prior-art liquid lenses to conform each microscope's performance to a desired set of specifications. In addition to adjusting the focus of each microscope on the fly to conform to variations in the sample surface, the invention allows for corrective action to be taken dynamically during use of the array microscope, thereby allowing total flexibility and programmable versatility to correct for aberrations in the array so that the various microscopes perform uniformly.